The present invention is directed to a method of preparing dried fruits which method does not utilize sulfurous containing compounds as preservative agents. More particularly, the present invention is directed to a method of preparing dried fruits which does not utilize any sulfiting agents in order to prevent enzymatic and non-enzymatic browning and further to inhibit microbiological activity.
Dried fruits are a popular snack food item. Besides being very tasty, dried fruits contain many vitamins and minerals. Consequently, in comparison to many other snack foods, dried fruits provide a healthy alternative. However, one problem that has existed over the years with regard to dried fruits is that they have usually undergone a sulfiting treatment in order to control the enzymatic and non-enzymatic browning of the fruit and also to slow down or inhibit any microbiological activity in the fruit. There is no doubt that sulfiting is a very effective technique for the preservation of dried fruits. Sulfiting consists of treating the fruits with sulfur dioxide or with sulfurous acid salts. The sulfurous acid salts that are utilized are usually the alkali metal salts of the bisulfite ion and of the metabisulfite ion. The treatment can also be by directly utilizing sulfur dioxide.
Sulfiting acts to prevent non-enzymatic browning by inhibiting the Maillard reaction. In Maillard reaction browning there is a reaction between the reducing sugars in the fruit and the amino acids or amino compounds of the fruit. In this reaction, there is formed an intermediate Schiff base. This Schiff base intermediate then undergoes further reaction to ultimately form the brown pigment which is indicative of non-enzymatic browning. However, when the fruit has undergone sulfiting, the reducing sugars rather than undergoing reaction with the amino acids or amino compounds to produce the Schiff base, will undergo reaction with the sulfiting agent to produce an hydroxy sulfonate product. This sulfonate product intermediate will not further react to form the brown pigment that is indicative of non-enzymatic browning. Enzymatic browning also is inhibited by sulfiting agents in that the sulfiting agent will act as an inhibitor vis-a-vis the enzyme which causes the browning. The exact mechanism is not known but it is known that in the presence of the sulfiting agents the enzymes become deactivated. Further, sulfiting agents prevent the oxidative deterioration of the dried fruit. The reason for this is that the sulfiting agents are reducing agents. Since they are reducing agents the sulfiting agents can scavenge any dissolved oxygen and thereby prevent oxidative deterioration. The sulfiting agents are also effective in preventing the growth of microorganisms.
In addition to the above uses of sulfiting agents, sulfiting agents have also been found to be effective during the steeping of corn, in preventing potatoes from souring during potato starch manufacturing, in the bleaching of cherries for maraschino cherry production, to prevent the racemization and discoloration of corn syrup, to improve the color retention of garbanzo beans, to preserve the color of canned green beans, to lengthen the life of ripe tomatoes and to prevent the discoloration of coconut. These are only some of the beneficial usages of sulfiting agents. There is no denying that sulfiting agents have been very effective in the preservation of various food products. However, sulfiting agents do present some problems. There are a number of individuals that are sulfite sensitive. Some of these people are asthmatics. For some of these people the ingestion of a sulfiting agent can lead to a very serious reaction. In some cases this serious reaction can be life threatening. It is for this reason that there is a search for effective techniques for the preparation and the preservation of dried fruits without the need to use sulfiting agents. If an acceptable method of treating fruits during the drying process can be found which does not require the use of sulfiting agents, it is believed that many consumers will purchase such dried fruits in place of those which have undergone a sulfiting treatment.
Various techniques have been tried over the years to preserve dried fruits without having to use sulfiting agents. In U.S. Pat. No. 3,754,938 there is disclosed a technique for preserving apple slices using a solution consisting of ascorbic acid, calcium chloride and sodium bicarbonate. The sodium bicarbonate is added to maintain a pH of 7 to 9 during treatment. When this treating solution is used it is disclosed that a sulfiting treatment does not have to be used.
U.S. Pat. No. 3,894,157 discloses a method for stabilizing the color of freeze-dried carrots by treatment with ascorbic acid or erythorbic acid. These acids are noted to be anti-oxidants. An aqueous solution containing one of these acids is sprayed onto the carrots. When ascorbic acid is the acid, the ascorbic acid is in a concentration of about 1 to 3 percent of the solution. The treated carrots are then freeze-dried.
U.S. Pat. No. 4,011,348 discloses the treatment of raw fruits and vegetables with an aqueous solution having a pH between about 4 and 1.5 and containing a selective ascorbate ion concentration. The ascorbate ion is provided by sodium ascorbate and ascorbic acid. However, it is directed that ascorbic acid should not be used alone since it results in an excessively low pH.
U.S. Pat. No. 4,504,504 discloses a technique for preserving the texture of diced fresh foods through the use of gelled polyuronic acids. This is stated to be superior to the use of citric acid or calcium chloride in preserving dried fresh food products.
U.S. Pat. No. 4,650,686 discloses a method for reducing excessive browning in a baked good containing reducing sugars. This is accomplished by adding to the dough baking soda and fatty acid monoglyceride esters of polycarboxylic acids. The agents minimize reducing sugar browning during the baking process.
In U.S. Pat. No. 2,344,151 there is disclosed a method and apparatus for treating perishable food items such as lettuce and various fruits. The process consists of precooling the food item. During this stage the food items are usually packed in their shipping crates. The process is particularly described with regard to lettuce. After the precooling, a vacuum is rapidly drawn which removes air and other substances from the food product. A certain amount of water and moisture is also removed. When a predetermined temperature is reached, a protective substance is drawn into the chamber by at least partially drawing down the vacuum in the chamber. The protective substance can be an edible mineral oil or substances such as lithium chloride, or calcium chloride. These are the substances to preserve lettuce. Other substances could be used to preserve other vegetables and fruits.
In U.S. Pat. No. 2,134,924 there is disclosed a method for sterilizing various food items. The technique that is disclosed is to subject the food item to a reduced pressure in a vacuum chamber and then, when the food item is at a reduced pressure in the vacuum chamber, introducing the preservative chemical agent into the vacuum chamber. The various chemical agents that are introduced into the vacuum chamber are utilized to attack infectious organisms, their eggs, larvae, spores, bacteria and the like. The chemical agents that are utilized are introduced into the vacuum chamber in the gaseous state. The objective of this patent is to treat a fruit or other food item with a gaseous sterilant and not with any liquid substances.
The present process is directed to a multi-step process for producing a dried fruit which has an extended shelf life and which has not undergone a sulfiting treatment. That is, the present process is an effective alternative to the use of sulfiting agents in order to preserve fruits while they are being processed and dried and further, later, when they are packaged. Further, there is no deterioration in the flavor of the fruit. This is advantageous because there is now a technique for producing sulfite free dried fruits having a fresh fruit taste.